Hydrogen phosphonates

ABSTRACT

The present invention relates to cyclic phosphorus compounds and processes for the preparation thereof. 
     The present invention relates to a process for the preparation of certain derivatives of cyclic hydrogenphosphonates which are diisocyanate derivatives formed as adducts or as polymers. 
     The cyclic phosphorus compounds are useful as flame retardants with organic polymers, such as polyurethanes, polyesters, and polyamides.

BACKGROUND OF THE INVENTION

The present invention relates to cyclic phosphorus compounds, such ascertain cyclic hydrogen phosphonate derivatives, processes for thepreparation of such compounds and their derivatives and to flameretardant compositions containing the said cyclic phosphorus compounds.

Certain phosphonates have been employed as flame retardant additives,but have suffered from the defect of causing undesirable crosslinking ofpolymeric materials in which the phosphonates were employed. Forexample, the addition of such phosphonates to a molten polymer such aspolyethylene terephthalate or a nylon, preliminary to the extrusion orspinning step has shown that the crosslinking prevents the formation ofacceptable fibers. As a result of the crosslinking, the fibers containlumps and irregular sections so that the extrusion through spinnerettesis hampered and the stretching, washing and other physical treatments ofthe fiber become impossible.

It has now however been found that certain cyclic phosphorus compoundsincluding cyclic phosphonates are particularly useful as flameretardants for organic polymeric materials. The invention includescombinations of the present cyclic phosphorus compounds together withorganic polymers such as polyurethanes, polyesters, e.g. polyethyleneterephthalate, and polyamides e.g., the nylons.

SUMMARY OF THE INVENTION

The general formulae for the cyclic phosphorus derivatives of theinvention are: ##STR1## where R is selected from the group consisting ofalkylene or alkyl substituted alkylenes of 2 to 20 carbon atoms, orarylene and alkyl substituted arylenes of 6 to 22 carbon atoms. Thepolymer has a degree of aggregation of 2 to 100.

The above compounds are derivatives of cyclic hydrogen-phosphonates.They are obtained by the reaction of a crude or purified hydrogenphosphonate with a diisocyanate.

Representative examples of diisocyanates are 4,4'-diphenylmethanediisocyanate; butylene diisocyanate; propylenediisocyanate; octadecylenediisocyanate; hexamethylene diisocyanate; tolylene-2,4-diisocyanate;isophorone diisocyanate; and 2,2,4-(2,4,4-) trimethylhexamethylenediisocyanate.

The general reactions for the preparation of the diisocyanatederivatives as adducts (first equation based upon mono hydrogenphosphonates as reactants), or as polymers (second equation based upondihydrogen phosphonates) are: ##STR2## where R is the same as above.Examples of R include butylene, phenylene, and tolylene.

The present cyclic phosphorus compounds of the invention, existing asadducts or polymers are useful per se as flame retardant materials whichprovide phosphorus as a component to reduce flammability. Improvement inflame retardant properties result when the present derivatives are usedwith organic polymers. Such resultant products do not burn readily, andinstead inhibit flammability of an organic polymer, for instance apolyurethane which is useful in the production of an elastomer or arigid or flexible foam. An example of an elastomeric polyurethane is theproduct obtained by heating together poly(tetramethylene ether)glycoland methylene bis(p-phenylisocyanate).

The cyclic phosphorus compounds including the cyclic hydrogenphosphonates of the present invention are useful as flame retardantmodifiers for organic polymers. These compounds can be added directly tothe molten polymer or the components of a foam composition beforepolymerization, e.g. before spinning fibers or forming films or othershaped objects including foamed plastics. Typical polymers arepolyesters, polyamides, polyurethanes, polyolefins, nitrile polymerssuch as polyacrylonitrile, vinyl polymers such as vinyl chloride,styrene polymers and copolymers such as acrylonitrile-butadiene-styrenecompositions.

The general reaction of the process for the production of hydrogenphosphonates that are useful in the practice of the present invention isbased upon the use of formic acid with a cyclic phosphorohalidite, suchas a phosphorochloridite, represented in the process below by thestructure, ##STR3## where R' is an alkylene, or haloalkylene group of a1,2-glycol having from 2 to 8 carbon atoms, or of a 1,3 glycol havingfrom 3 to 8 carbon atoms, and X is Cl or Br. An example is: ##STR4##Examples of specific useful phosphorochloridites are thebis-(phosphorochloridites), such as3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, ##STR5##and the corresponding bromo derivative;

2-chloro-5,5-bis(bromomethyl)-1,3,2-dioxaphosphorinane, ##STR6## and therelated phosphorochloridites,2-chloro-5,5-dimethyl-1,3,2-dioxaphosphorinane, and2-chloro-5-ethyl-5-methyl-1,3,2-dioxaphosphorinane, and2-bromo-5,5-bis(chloromethyl)-1,3,2-dioxaphosphorinane, and2-chloro-5-phenyl-1,3,2-dioxaphosphorinane, and2-chloro-5-(4-fluoro-3-bromophenyl)-1,3,2-dioxaphosphorinane.

The process of converting cyclic phosphorochloridites to cyclic hydrogenphosphonates can also be applied to five-membered ringphosphorochloridites, e.g.,4,5-dimethyl-2-chloro-1,3,2-dioxaphospholane,2-chloro-1,3,2-dioxaphospholane, 2-butyl-1,3,2-dioxaphospholane,4-chloromethyl-1,3,2-dioxaphospholane, and4-methyl-1,3,2-dioxaphospholane.

The method of treating cyclic phosphorochloridites with formic acidprovides an improved process for producing cyclic hydrogenphosphonates,sometimes called cyclic phosphites. Some earlier workers in this area ofphosphorus chemistry have also called these compounds cyclic hydrogenphosphites, but preferable general terminology is to call thesecompounds cyclic hydrogenphosphonates because it better describes thepredominant pentavalent state of the phosphorus. A number of methods areknown for preparing cyclic hydrogenphosphonates, such as the use oftriethylamine as an acid-binding agent in the hydrolysis of cyclicchlorophosphites (cyclic phosphorochloridites). In this procedure, anamine hydrochloride is produced as a by-product, and this must then beseparated from the desired cyclic hydrogenphosphonate.

In the above process, using formic acid instead of water, theby-products are anhydrous hydrogen chloride and carbon monoxide, gaseousproducts which are easily removed, leaving the easily isolated cyclichydrogenphosphonate. For example, when attempts were made to prepare3,9-H-3,9-dioxo-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane(I),##STR7## by treatment of3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphospiro[5.5]undecane withwater by the prior art procedures, none of the desired product could beisolated from the mixture of side reaction products. However, whenformic acid is used according to the present invention, essentially pureand easily isolated compound I is obtained.

Catalysts are unnecessary in the above process for preparing hydrogenphosphonates. A solvent is generally unnecessary when formic acid isused for conversion of cyclic phosphorochloridites to cyclichydrogenphosphonates. Inert solvents or suspending liquids, e.g.acetonitrile, benzene, and 1,2-dichloroethane, can however be used toaid mixing and temperature control.

The reaction is usually carried out by the addition of formic acid tothe stirred phosphorochloridite at 10° to 100° C, preferably 30° to 70°C, while allowing the by-products hydrogen chloride (or hydrogenbromide) and carbon monoxide to be expelled through a condenser and thentrapped or absorbed by suitable and safe methods such as neutralization.In one case, this mixture of gases is passed into a stirred suspensionof aluminum trichloride and toluene to produce p-tolualdehyde by theGatterman-Koch Reaction, thus confirming the composition of the effluentgases and demonstrating a practical by-product recovery application.

The process for the preparation of the said derivatives as adducts, orpolymers by treating a hydrogenphosphonate with a diisocyanate iscarried out at 0° C to 100° C. No solvent is necessary, although inertsolvents such as benzene, toluene and chlorobenzene may be used.

For this process, a basic catalyst is desirable. Examples of typicaluseful basic catalysts are, e.g. the heterocyclic nitrogen bases such asN-methylmorpholine, pyridine, quinoline, N-ethylpiperidine, picoline,quinaldine, 4-methylpyrimidine, or N-phenylpyrazole; the tertiary aminessuch as triethylamine, trimethylamine, tri-tert-butylamine,N,N-dimethylaniline and N-benzyl-N-methylaniline; alkylene polyaminessuch as triethylenediamine; quaternary ammonium compounds such asbenzyltrimethylammonium methoxide or tetrabutylammonium butoxide; alkalimetal alkoxides such as sodium or potassium methoxide, etc. The quantityof catalyst to be used will depend upon the nature of the specificdisocyanate and cyclic hydrogenphosphonate; obviously the more reactivereactants will require less catalysts than will the somewhat moresluggish reaction compounds. Whether or not a diluent is used willlikewise regulate catalyst quantity. Also variable is the temperature atwhich reaction is effected; for, here again must be taken intoconsideration the nature of the reactants, catalyst quantity, andwhether or not a diluent is used. The reaction is generally exothermic;hence the present addition reactions can be conducted at ordinary roomtemperature or even at decreased temperatures, but heating of thereaction mixture may be needed to complete the reaction. All of thesevariables, i.e. catalyst quantity, use of diluent and temperatureconditions can readily be arrived at by easy experimentation.

The compounds of the present invention are useful in flame-retardantmaterials. The method of testing flame-retardant properties is A.S.T.M.Designation D 2863-70, entitled "Standard Method of Test forFlammability of Plastics Using the Oxygen Index Method."

In the oxygen index (OI) testing procedure the relative flammability ofa plastic material such as nylon, or polyethylene terephthalate isdetermined by measuring the minimum concentration of oxygen in a slowlyrising mixture of oxygen and nitrogen that will just support combustion.Consequently the oxygen index expresses such minimum concentration ofoxygen, expressed as volume percent, in a mixture of oxygen and nitrogenthat will just support combustion.

The test is conducted by burning the material in a test column which isa heat resistant glass tube of 75 mm minimum inside diameter and 450 mmminimum height. At the bottom of the tube is a bed of glass beads about100mm deep to mix and distribute the gas mixture. Within the glass tubeused as the test column there is a specimen holder to support thetreated plastic material while the apparatus is supplied with oxygen andnitrogen flow and control devices. The apparatus is also provided withan igniter which is a separate tube through which a combustible gas suchas natural as is used to ignite the test specimen. In the presenttesting program glass scrim supported molded sheets of nylon orpolyethylene terephthalate ca. 0.2mm thick and about 25mm by 100mm insize are used as the test specimens which are prepared from nylon orpolyethylene terephthalate powder and 1% to 20° by weight of the fireretardant additive; the data in the present work correspond to about 10%by weight of additive. As a result of the molding of the organicpolymer, e.g. nylon or polyethylene terephthalate, and the additive, andintimate admixture or melt of the molecules of the components isobtained.

In conducting the test, the specimen is clamped in the holder in thetest column after which the desired initial concentration of oxygen isintroduced to the ignited specimen. A number of tests are conducted todetermine the minimum concentration of oxygen that will just supportcombustion.

The present condensation products are useful in combination with organicpolymers generally to reduce combustibility. The normally flammableorganic polymers which are rendered fire retardant in accordance withthe invention may be natural or synthetic but are preferably a solidsynthetic polymer, more preferably a nylon or ester type polymer.Examples of the polymers are cotton, wool, silk, paper, natural rubber,and paint, and also the high molecular weight homopolymers andcopolymers of amides, e.g., (nylon 66 and nylon 6). Other polymersinclude esters such as polyethylene terephthalate, and polymers of otherunsaturated aliphatic and aromatic hydrocarbons, e.g. ethylene,propylene, butylene, styrene, etc., and also acrylic polymers, e.g.,polyacrylonitrile, polymethyl methacrylate, alkyd resins, as well ascellulose derivatives, e.g., cellulose acetate, methyl cellulose, etc.Still other polymers include epoxy resins, furan resins, isocyanateresins such as polyurethanes, melamine resins, vinyl resins such aspolyvinyl acetate and polyvinyl chloride, resorcinol resins, syntheticrubbers such as polyisoprene, polybutadiene-acrylonitrile copolymers,butadiene-styrene polymers, butyl rubber, neoprene rubber, ABS resinsand mixtures thereof. Since the compositions of the invention areunusually effective flame retardants they are normally combined in flameretarding proportions with the organic polymer at relatively lowconcentrations, e.g., about 1-20 wt. %, preferably about 3-15% based onadditive plus the polymeric substrate, such as by milling, orimpregnation, e.g., from a water or alcohol dispersion or solution or bydissolving or dispersing in the molten polymer before extrusion such asin the form of fibers or sheets. It should be noted that it is withinthe scope of the invention to incorporate such ingredients as dyes,pigments, stabilizers, antioxidants, antistatic agents and the like intothe novel compositions.

The cyclic phosphorus compounds of the invention have a lesser tendencyto cause cross linking than prior phosphonate flame retardants.

The following examples illustrate embodiments of the invention but arenot restrictive.

EXAMPLE 1

A reaction vessel is charged with 272 grams (2.0 moles) ofpentaerythritol, 567 grams of phosphorus trichloride, 0.1 gram ofpyridine hydrochloride, and 272 grams of ortho-dichlorobenzene as asolvent. This mixture is warmed to 100° C in 2 hrs. and kept at100°-105° C for one hour, giving a clear, colorless solution having a ³¹P nmr signal at -149 ppm for the cyclic phosphorochloridite,3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane. Thisintermediate is converted to the hydrogenphosphonate by dropwiseaddition of 184 grams (4 moles) of 97-100% formic acid over a 65 minuteperiod. The temperature is maintained at about 25°-42° C during theaddition. A stream of gaseous nitrogen is passed through the stirredreaction mixture until most of the by-product HCl and CO have been sweptout. The reaction mixture is filtered to remove solids which are thenwashed with benzene, followed by acetonitrile and ether. The white solidproduct, ³¹ P nmr-6.4(d,J_(PH) =696 cps), is3,9-H-3,9-dioxa-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane havingthe formula shown below: ##STR8##

Analysis: Calcd. for C₅ H₁₀ O₆ P₂ (percent): C, 26.33; H, 4.42; P,27.16. Found: C, 26.17; H, 4.76; P, 26.77.

The use of PBr₃ instead of PCl₃ leads to the same product.

EXAMPLE 2

Phosphorus trichloride, 274.8 g (2.0 moles), is added dropwise to astirred solution of 524g. (2.0 moles) of2,2-di(bromomethyl)-1,3-propanediol and 0.2g. of pyridine hydrochloridein 600 g. of benzene during 2.5 hrs. with enough warming to keep thetemperature above 20° C. After several hours of stirring at roomtemperature, a ³¹ P nmr spectrum of the reaction mixture shows a peakfor 90% of the phosphorus at -146.6 ppm for2-chloro-5,5-di(bromomethyl)-1,3,2-dioxaphosphorinane.

Stirring of the reaction mixture is continued as 106 g. (2.3 moles) offormic acid is added at room temperature during 2 hrs., followed bywarming at 45° C. for 1.5 hrs. A solid product separates on cooling.This is recrystallized from benzene, giving 333 g. of white solid, m.p.91°-96°, ³¹ P nmr -5.2 ppm (d, J_(PH) =695 cps), which is the cyclichydrogenphosphonate,5,5-bis(bromomethyl)-2-H-2-oxo-1,3,2-dioxaphosphorinane, having thestructure, ##STR9##

EXAMPLE 3

A mixture of 0.1 mole of the product of Example 2 and 0.05mole of1,6-diisocyantohexane in 100 g. of benzene is stirred as 30 drops oftriethylamine is added at 23°-32° C. The reaction mixture is warmed at50°-60° for 0.5 hr. and then filtered. The solid product is washed withwarm benzene and acetone, giving 31.3g of white solid, m.p. 198°-206°,³¹ P nmr 8.5 ppm, which is5,5,5',5'-tetrakis(bromomethyl)-N,N'-hexamethylene-bis(2,2'-dioxo-1,3,2-dioxaphosphorinane-2-carboxamide),##STR10##

Analysis -- Calcd. for C₁₈ H₃₀ Br₄ N₂ O₈ P₂ : C, 27.57; H, 3.86; Br,40.76; N, 3.57; P, 7.90. Found: C, 27.89; H, 3.69; Br, 41.08; N, 3.57;P, 7.85.

EXAMPLE 4

Similarly, 0.1 mole of the product of Example 2 and 0.05mole oftolylene-2,4-diisocyanate gives 33.5 g. of white solid, m.p. 199°-210°C, ³¹ P nmr 8.9 ppm, which is5,5,5',5'-tetrakis(bromomethyl)-N,N'-(o-methylphenylene)-bis(2,2'dioxo-1,3,2-dioxaphosphorinane-2-carboxamide).

Analysis -- Calcd. for C₁₉ H₂₄ Br₄ N₂ O₈ P₂ : C, 28.89; H, 3.06; Br,40.46; N, 3.55; P, 7.84. Found: C, 28.54; H, 3.03; Br, 39.94; N, 3.50;P, 7.72.

Other examples of diisocyanates that give analogous cyclic phosphorusadducts are 4,4'-diphenylmethane diisocyanate; butylene diisocyanate;propylene diisocyanate; octadecylene diisocyanate; hexamethylenediisocyanate; isophorone diisocyanate and2,2,4-(2,4,4-)trimethylhexamethylene diisocyanate.

EXAMPLE 5

A mixture of 0.1 mole of the product of Example 1 and 0.1 mole ofhexamethylenediisocyanate in 200 ml of dimethylformamide is stirred as40 drops of triethylamine is added. A mildly exothermic reaction occurs,causing a temperature rise from 24° to 32° C. The reaction mixture iswarmed at 70°-80° for 0.5 hr, and then 250 ml of acetonitrile is addedin 10 minutes, causing a white polymer to separate. The mixture iswarmed at 75° for 1 hr, and then it is filtered while hot. The whitesolid is extracted with hot acetonitrile and acetone and dried at100°/0.15 mm, giving 31.1 g. of white powder which is a polymer havingthe structure, ##STR11##

It can be molded at 230°-240° C and 20,000 psi.

EXAMPLE 6

Similarly to the preceding example, a polymer is prepared from 0.1 moleeach of the product of Example 1 and tolylene-2,4-diisocyanate indimethylformamide using triethylamine as a catalyst to promotepolymerization.

Other examples of diisocyanates that give analogous cyclic phosphoruspolymers are 4,4'-diphenylmethane diisocyanate; butylene diisocyanate;propylene diisocyanate; octadecylene diisocyanate;tolylene-2,4-diisocyanate; isophorone diisocyanate and 2,2,4-(2,4,4-)trimethylhexamethylene diisocyanate.

EXAMPLE 7

Flame retardancy tests are conducted using typical compounds of theinvention, specifically the compounds of the above examples. Thesecompounds do not burn readily when subjected to heat and a flame; theyalso improve the flame retardant properties of polyamides, specificallynylon-6,6 and of polyethylene terephthalate, at concentrations of 1-20%by weight, preferably 3-15% by weight, based upon the total mixture,obtained such as by milling, or impregnation or by dissolving ordispersing in the polymer in molten form before extrusion such as in theform of fibers or sheets. It should be noted that it is within the scopeof the invention to incorporate such ingredients as dyes, pigments,stabilizers antioxidants, antistatic agents, and the like into the novelcompositions.

Test data of the oxygen index test described above for certain compoundsare set forth below:

    ______________________________________                                        Compound of                                                                   Example       O-I Value (10% additive)                                        ______________________________________                                        3             25.3                                                            4             25.2                                                            5             23.0                                                            6             25.3                                                            ______________________________________                                    

The present diisocyanate derivatives, as a group have flame retardantproperties for polyethylene terephalate and polyamides such as nylon6,6.

What is claimed is:
 1. A cyclic phosphorus composition ##STR12## where Ris selected from the group consisting of alkylene and alkyl substitutedalkylenes of 2 to 20 carbon atoms, or is selected from the groupconsisting of arylene and alkyl substituted arylenes of 6 to 22 carbonatoms.
 2. A cyclic phosphorus composition ##STR13## with --H and --NCOend groups, and having a degree of aggregation of 2 to 100, where R isselected from the group consisting of alkylene and alkyl substitutedalkylenes of 2 to 20 carbon atoms, or is selected from the groupconsisting of arylene and alkyl substituted arylenes of 6 to 22 carbonatoms.
 3. The composition of matter ##STR14##
 4. The composition ofmatter ##STR15## with --H and --NCO end groups, and having a degree ofaggregation of 2 to
 100. 5. Process for preparing a cyclic phosphoruscomposition which comprises admixing formic acid with a cyclicphosphorochloridite, having the formula ##STR16## where R' is analkylene, or a haloalkylene group of a 1,2-glycol having from 2 to 8carbon atoms, or of a 1,3-glycol having from 3 to 8 carbon atoms, and Xis Cl or Br, at 10°-100° C and thereafter treating the resultingintermediate with a diisocyanate.
 6. The combination of an organicpolymer together with ##STR17## where R is selected from the groupconsisting of alkylene and alkyl substituted alkylenes of 2 to 20 carbonatoms, or is selected from the group consisting of arylene and alkylsubstituted arylenes of 6 to 22 carbon atoms.
 7. The combination of anorganic polymer together with ##STR18## with --H and --NCO end groups,and having a degree of aggregation of 2 to 100,where R is selected fromthe group consisting of alkylene and alkyl substituted alkylenes of 2 to20 carbon atoms, or is selected from the group consisting of arylene andalkyl substituted arylenes of 6 to 22 carbon atoms.
 8. The combinationof an organic polymer together with ##STR19##
 9. The combination of anorganic polymer together with ##STR20## with --H and --NCO end groups,and having a degree of aggregation of 2 to 100,where R is selected fromthe group consisting of alkylene or alkyl substituted alkylenes of 2 to20 carbon atoms, or arylene and alkyl substituted arylenes of 6 to 22carbon atoms.